The surfaces of the existing off road paths needs to be improved.
Sustrans experience informs us that to handle cyclists, walkers, mobility scooters and equestrian users we need to use a sealed surface.
The surface needs to be smooth (but not slippery for horses hooves) for cycling and mobility scooters, well drained (a specific issue in some places) and ideally 3 metres wide.
The considered wisdom is that the surface needs to be bitumen macadam or asphalt. The Sustrans Design Manual shows the way this can be achieved.(See link below). But there are other solutions
In France they use stabilised sand that provides a surface that drains well, is hard wearing, lighter than normal sand and bound with cement. It is also much more environmentally friendly. This needs investigation as sand is a local raw material.